Manufacture of crimped viscose rayon fibres



United States Patent C) M 3,340,340 MANUFACTURE OF CRMPED VISCOSE RAYONFIBRES Ernest Mytum, Warwick, England, Assignor to Courtaulds Limited,London, England, a British company No Drawing. Filed Dec. 3, 1963, Ser.No. 327,818

Claims priority, application Great Britain, Dec. 11, 1962, 46,652/62 3Claims. (Cl. 264-168) This invention is concerned with the manufactureof grilmped viscose rayon fibres having enhanced extensii 'ty.

United States patent specification No. 2,986,446 describes a process forthe manufacture of crimped viscose rayon fibres by extruding a viscosecontaining polyethylene glycol into an acid coagulating and regeneratingbath containing zinc sulphate, stretching the filaments so formed andrelaxing the stretched filaments in an aqueous medium. The importantproperties of crimp and extensibility of the filament can be controlledby a change in one or more of the inherent features of the process, but,in general, a change which causes an increase in one property has theeffect of decreasing the other. For example, the degree of crimpincreases and the extensibility decreases when the filament is stretchedmore, whilst an increase in the zinc sulphate concentration in the bathincreases the extensibility of the filament but decreases the degree ofcrimp. The properties of the filament can, therefore, be varied betweenhigh degree of crimp and low extension on the one hand and highextension and low degree of crimp on the other. The process is, however,incapable of producing a filament which combines the features of highdegree of crimp and high extension.

Crimped staple fibres may be used as the pile of carpets. For this use,the fibres should be extensible, as this contributes to their resistanceto abrasion, and resilient, to preserve the appearance of the carpetduring wear. Viscose rayon fibres can be made more resilient bycross-linking the constituent cellulose, but this modification causes adecrease in extensibility. A viscose rayon fibre suitable forcross-linking and use in carpet piles, should, therefore, be highlyextensible so as to be able to tolerate the inevitable fall inextensibility which accompanies crosslinking and still retain sufiicientextensibility to maintain the resistance to abrasion.

I have devised a process for the manufacture of crimped viscose rayonfibres having an increased extensibility.

According to the present invention a process for the production ofcrimped viscose rayon fibres comprises extruding a viscose containingfrom 5 percent to percent of cellulose, from 5 percent to 10 percent ofcaustic soda, more than 0.05 percent of a modifier and a zinc compoundin the proportion of from 0.01 percent to 0.8 percent of zinc based onthe weight of the viscose, at a salt figure of between 3 and 14, into acoagulating and regenerating bath containing from 5 percent to 14percent of sulphuric acid, from 0.5 percent to 4 percent of zincsulphate and more than 12 percent of sodium sulphate, to formincompletely regenerated filaments, stretching the filaments by at least50 percent, cutting the stretched filaments into staple fibres andcrimping the fibres by relaxing the fibres in a solution containingbetween 1 percent and 5 percent of caustic soda, before completing theregeneration of the cellulose in the fibres.

The increase in the extensibility of the fibre, is due, in the main, totwo additions to the acknowledged, known process. The first of these isthe use of a zinc compound, preferably an alkali metal zincate, in theviscose. This allows a desired degree of crimp to be obtained from alower stretch, thus preserving to a greater extent the extensibility ofthe fibre. The effect is noticeable even 3,340,340 Patented Sept. 5,1967 when the zinc sulphate concentration in the bath is high, that isat or near 4 percent and, thus, the zinc in the viscose can be used toreduce the antagonistic action of zinc in the bath to the crimp in thefibre.

The second addition is that of relaxing the incompletely regeneratedfibre in a dilute caustic soda solution. This has a remarkable elfect onthe extensibility, causing increases of as much as 50 percent of thepreexisting extensibility without deleteriously affecting the degree ofcrimp. The relaxation of dried cellulose fibres in caustic sodasolutions is a process which can only achieve increases of the order of10 percent in the extensibility of the fibres, and the process is lessefiicient than that of similarly treating the incompletely regeneratedfibre.

Once the incompletely regenerated fibre has been rendered alkaline inthe relaxing step, the regeneration of the cellulose is moreeconomically accomplished by continuing to treat the fibre with causticsoda, which hydrolyses the xanthate groups, rather than by reverting toan acid environment, in which the regeneration is due to the decay offree xanthic acid groups. The change over from alkaline to acidconditions obviously involves the consumption of both acid and alkali.The principle of alkaline regeneration is applicable in the manufactureof all kinds of viscose rayon fibres, but, in general, is useful onlywhere an essential alkaline treatment follows the acid coagulation step.

In a preferred form, the invention consists in extruding a viscosecontaining from 7.5 percent to 8.3 percent of cellulose, caustic sodasuch that the ratio of caustic soda to cellulose is between 0.7 and 0.9,0.1 percent to 0.3 percent of polyethylene glycol having an averagemolecular weight of between 600 and 6,000 and a zinc compound in aproportion of from 0.04 percent to 0.2 percent of zinc based on theweight of the viscose, at a salt figure of from 5.5 to 8.5, into acoagulating and'regenerating bath containing sulphuric acid in aconcentration of from 1.0 to 1.4 times the caustic soda content of theviscose, from 1 to 2 percent of zinc sulphate and between 22 and 24percent of sodium sulphate, to form incompletely regenerated filaments,stretching the filaments by at least 60 percent of their original lengthin air, cutting the filaments into staple fibres and crimping the fibresby suspending the fibres in a solution containing between 1.5 and 2.5percent of caustic soda, before completely regenerating the fibres.

The invention is illustrated by the following example in whichpercentages are by weight.

Example 1 A viscose containing 8.3 percent of cellulose, 6.2 percent ofcaustic soda, 0.166 percent of polyethylene glycol having an averagemolecular weight of 1,500, and 0.22 percent of sodium zincate wasextruded at a salt figure of 6 into a regenerating bath containing 7.8percent of sulphuric acid, 24.0 percent of sodium sulphate and 1.8percent of zinc sulphate. The filaments so formed were withdrawn fromthe bath, stretched in air by 70 percent of their original length, cutinto staple fibres and dropped into a solution containing 2 percent ofcaustic soda where they remained for 5 minutes. The fibres were thenseparated from the solution in a rotary extractor, washed, impregnatedwith acid, washed again, finished and dried.

The corresponding properties of a fibre produced by the process fromwhich the caustic soda relaxation was omitted, were:

Air dry tenacity g./d 2.32 Air dry extensibility percent 25.3 Wettenacity g./d 1.23 Wet extensibility percent 35.2 Waves/cm. 2.7

and when this fully regenerated fibre was treated with 2 percent causticsoda, washed and dried, the properties became:

1. A process for the production of crimped viscose rayon fiberscomprising extruding a viscose containing from percent to percent ofcellulose, from 5 percent to 10 percent of caustic soda, more than 0.05percent of; a modifier and an alkali metal zincate in the proportion offrom 0.01 percent to 0.8 percent of zinc based on the weight of theviscose, at a salt figure of between 3 and 14, into a coagulating andregenerating bath containing from 5 percent to 14 percent of sulphuricacid, from 0.5 percent to 4 percent of Zinc sulphate and more than 12percent of sodium sulphate, to form incompletely regenerated filaments,stretching the filaments by at least 50 peIcent cutting the stretchedfilaments into staple fibres and crimping the fibres by relaxing thefibres in a solution containing between 1 percent and 5 percent ofcaustic soda, before completing the regeneration of the cellulose in thefibres.

2. A process comprising extruding a viscose contain ing from 7.5 percentto 8.3 percent ofcellulose, caustic soda such that the ratio of causticsoda to cellulose is between 0.7 and 0.9, 0.1 percent to 0.3 percent ofpolyethylene glycol having an average molecular weight of between 600and 6,000 and an alkali metal zincate in a proportion of from 0.04percent to 0.2 percent of zinc based on the Weight of the viscose, at asalt figurev of from 5.5 to 8.5, into a coagulating and regeneratingbath containing sulphuric acid in a concentration of from 1.0 to 1.4times the caustic soda content of the viscose, from 1 to 2 percent ofzinc sulphate and between 22 and 24 percent of sodium sulphate, to formincompletely regenerated filaments, stretching the filaments by at leastpercent of their original length in air, cutting the filaments intostaple fibres and crimping the fibres by suspending the fibres in asolution containing between 1.5 and 2.5 percent of caustic soda, beforecompletely regeneratin g the fibres.

3. A process as claimed in claim 2 in which the cellulose in the fibresis completely regenerated by contact with a caustic soda solution.

References Cited UNITED STATES PATENTS 2,515,834 7/1950 Nicoll 264168 X2,860,480 11/1958 Cox 264197 X 2,879,170 3/1959 Miller l06165 X2,966,391 12/1960 Bandel 264197 X 2,986,446 5/1961 Smith 264198 X3,046,083 7/ 1962 Baites et a1. 264-168 FOREIGN PATENTS 570,159 6/1945Great Britain.

ALEXANDER H. BRODMERKEL, Primary Examiner.

J. H. WOO, Assistant Examiner.

1. A PROCESS FOR THE PRODUCTION OF CRIMPED VISCOSE RAYON FIBERSCOMPRISING EXTRUDING A VISCOSE CONTAINING FROM 5 PERCENT TO 10 PERCENTOF CELLULOSE, FROM 5 PERCENT TO 10 PERCENT OF CAUSTIC SODA, MORE THAN0.05 PERCENT OF A MODIFIER AND AN ALKALI METAL ZINCATE IN THE PROPORTIONOF FROM 0.01 PERCENT TO 0.8 PERCENT OF ZINC BASED ON THE WEIGHT OF THEVISCOSE, AT A SALT FIGURE OF BETWEEN 3 AND 14, INTO A COAGULATING ANDREGENERATING BATH CONTAINING FROM 5 PERCENT TO 14 PERCENT OF SULPHURICACID, FROM 0.5 PERCENT TO 4 PERCENT OF ZINC SULPHATE AND MORE THAN 12PERCENT OF SODIUM SULPHATE, TO FORM INCOMPLETELY REGENERATED FILAMENTS,STRETCHING THE FILAMENTS BY AT LEAST 50 PERCENT, CUTTING THE STRETCHEDFILAMENTS INTO STAPLE FIBRES AND CRIMPING THE FIBRES BY RELAXING THEFIBRES IN A SOLUTION CONTAINING BETWEEN 1 PERCENT AND 5 PERCENT OFCAUSTIC SODA, BEFORE COMPLETING THE REGENERATION OF THE CELLULOSE IN THEFIBRES.